1. Field of the Invention
The invention relates generally to magnetic disk drives and more specifically to diskette formats in very high track density drives and systems.
2. Description of the Prior Art
Continual advances in floppy disk technology have allowed the rapid migration from eight inch, to 5.25 inch to 3.5 inch diskettes. Originally, 5.25 inch diskettes held only 360K bytes of data, but higher track densities and more efficient recording formats have allowed the smaller 3.5 inch diskette to store as much as 1.44M bytes in the recent high density (HD) format. Such rapid migration has caused severe interoperability concerns, because of the physical incompatibility between the traditional formats. Advances in floppy disk technology have not stayed still. By embedding optical servo information in an otherwise standard 3.5 inch micro-floppy diskette, storage capacities of twenty megabytes and beyond are possible. The Micro Standards Committee, sponsored by the Microcomputer Managers Association, announced at COMDEX/Spring 1989 a 10-month study of proposed new formats to replace the aging 1.44M byte diskette. (See, "Draft White Paper on a New Standard for Very-High-Density Diskette Drives," Feb. 5, 1990, published by the Micro Standards Committee, 50 W. 34th St., Suite 23C7, New York, N.Y. 10001.) The result was to recommend a 20.9M byte optical-magnetic format that was judged to be superior on every criterion rated.
Higher density disks have resulted from ever increasing track densities. The more concentric data tracks that can be packed into an area on a given disk size, the more data can be stored. But increasing track densities compound the problems in positioning a read/write head over the proper track. Stepper motors have been used in low track density drives to position the heads, but stepper motor positioning systems do not have the accuracy required for high track densities. Magnetic servo tracks embedded between data tracks or on a specialized surface in a multi-surface disk disk have also reached their limits. The prior art includes optical servo positioning methods that offer high track densities and good performance.